The proposed research is aimed at increasing the understanding of the mechanisms whereby nutrients are absorbed by the small intestine in higher animals. The transport properties of isolated intestinal plasma membranes will be characterized with respect to sugars, amino acids, and electrolytes. The studies will concentrate on an understanding of the coupling between the process of active nutrient absorption and metabolic energy. The differences in transport mechanisms and kinetics of the various transport systems will be determined in the two plasma membranes of the polar intestinal epithelial cell, i.e. the microvillus (luminal) and the lateral-basal (antiluminal) plasma membrane. Furthermore, the role of hormones and other agents which regulate and influence intestinal transport will be evaluated through a characterization of the changes that these agents produce, directly or indirectly, in the transport properties of the isolated membranes. The increased knowledge resulting from this work about the absorptive process in physiological and pathological states is thought to be valuable for dietary treatments of diseased states and for nutrition in general. The studies are of obvious significance in so far as they relate to the pathophysiology of certain intestinal diseases, for example secretory states induced by bacterial toxins.